This invention relates generally to the field of synthetic resinous closures for containers of liquid beverages and the like under pressurized condition; and more particularly to an improved threaded closure incorporating a tamper-indicating ring which is severed from the remaining parts of the closure when the closure is first unthreaded from the container.
In recent years, this type of closure has been in increased commercial acceptance for use with synthetic resinous or glass containers, as contrasted with single use aluminum cans and the like, to replace the unthreaded crown type closure which cannot be used to reseal the container once it has been removed. However, the fact that the container may be resealed gives rise to the necessity of providing tamper-indicating means to assure the user of the integrity of the contents of the container.
Closures of this type have been manufactured using injection molding techniques in a variety of synthetic resinous material, typically, polyterephthalate (PET). More recently, particularly where the internal pressures of the container are not excessive, the closures are formed from relatively softer and less dense materials such as polyethylene. This material is somewhat easier to mold, and because of greater flexibility, the closure usually does not require a separate seam gasket on the inner surface of the end wall.
However, these advantages are not without accompanying complication. The material comprising the tamper-indicating ring is normally of relatively thin cross section, and during removal of the formed closure from the mold, it must be radially expanded to clear the thread-forming proclivities on the male part of the molding cavity. The closure is removed using an orificed ejection or stripping plate which engages the lower edge of the tamper-indicating ring, or other annularly projecting portion of the closure over at least a part of its inner surface to expand the closure to clear the projections on the outer surface of the male part of the mold. When using the above-mentioned softer synthetic resinous materials, the tamper-indicating ring which is frangibly interconnected to the body of the closure is often either separated or ruptured during this operation. It is normally not a problem when using materials of greater strength or density.